DeepDeep ImpactImpact thethe MovieMovie ScienceScience FactFact vs.vs. FictionFiction KKaarreenn JJ.. MMeeeecchh,, AAssttrroonnoommeerr IInnssttiittuuttee ffoorr AAssttrroonnoommyy SSeessssiioonn 3344 –– 11//1199//0055 SScciieennccee FFaacctt vvss.. FFiicctitioonn Deep Impact, the Movie Armageddon Themes: comet/asteroid is about to impact Earth What we can to to avert disaster DDeeeepp ImImppaacctt FFaacctsts Nucleus Split in two Diam1 = 1 mi r = 0.8km Diam2 = 6 mi r = 4.8km Rotation period 14 hr Earth collision r = 1AU WWhhaatt ththee MMoovviiee GGoott RRiigghhtt Comet Appearance Impact Energetics E = 0.5 m v2 v2 = GM(2/r – 1/a) Global consequences 1 km radius major 4.8 km catastrophic Radius [km] Mass [kg] KE [J] KE [Mton TNT] 0.8 2.2 x 1012 1.9x1019 3200 4.8 4.7x1014 4.1x1021 690,900 HHiisstotorriiccaall ImImppaacctsts Lunar evidence Barringer crater, AZ ~ 50,000 yr 1972 Fireball, Tetons HHiisstotorriiccaall ImImppaacctsts Tunguska (1908) 30m radius 8 km explosion area KT Impact (65 Myr) Crater 10-15 x meteorite size Extinction of 50% of species Storms and fires Atmospheric dust months to clear CChhiiccxxuulluubb CCrraatteerr –– YYuuccaattaann Crater discovered 1950’s oil survey drilling Ground water seeping limestone Cenotes Diam 145-180 km 10 km diam; 108 ton TNT GGlloobbaall EEffeffecctsts Debris into Atmosphere Greenhouse gases (CaCO3 = limestone) Forest fires & “Nuclear Winter” Yucatan during Cretaceous shallow sea Tsunami – 100m high wave CCrraateterrss oonn EEaarrthth WWhhaatt tthhee MMoovvieie GGoott WWrroonngg Observing with lights on Orbit determined from single data point WWhhaatt tthhee mmoovvieie ggoott WWrroonngg BBoouullddeerrss iinn TTaaiill Largest: cm-sized 3 acrit = c Q vth / ρg ρnuc R nuc OOuuttggaassssiinngg aatt ssuunnrriissee Heat slowly penetrates No instantaneous jets WWhhaatt tthhee mmoovvieie ggoott The tidal wave Impact velocity 70000mph wwrroonngg Tsunami 500-1000 km/hr Deepwater waveht 1km: 6-35m (10x @ 100 km) “runup” height greater Factor of 2-3 (conservative) Factor 25-40 Hawaii Empire state: 443.2m AArrmmaaggeeddddoonn Right: Thrusters for gravity Impact in Paris Wrong: All else Discovery TX-sized Comet or Asteroid? Scheduling HST Meteor stream radiants Particle size Distribution Asteroid “Composition” AArrmmaaggeeddddoonn ((ccoonntdtd)).. Composition: If asteroid (metal): Ni or Fe Density 7000 kg/m3 Easy to drill Form from differentiation No volatiles! CH4.